share

Looking Closely at Oligocene Climate

Changes in solar forcing caused by Earth's orbital motion not only have direct effects on climate but can also exert indirect effects on greenhouse gases such as CO2. Pälike et al. (p. 1894) assembled a detailed, 13-million-year—long record of oxygen and carbon isotopes that span the entire Oligocene, a key period of Earth's transformation from a warm world essentially free of high-latitude ice sheets to one with persistent glaciation in Antarctica. Using a box model of the carbon cycle, they show how the global carbon cycle can amplify long-term solar forcing and attenuate shorter-term ones in a manner controlled mainly by the residence time of carbon in the oceans.